Misinterpreting the spins of high-mass precessing binary black holes: insights from time-domain morphology

The gravitational-wave (GW) signal GW190521 was inferred to originate from a precessing, equal-mass, quasicircular binary black hole (BBH). Its detector-frame total mass of ~270 solar masses places GW190521 at the edge of current GW detectors' sensitivity, leading to only a few observable cycles. Such short data offer alternative explanations: GW190521's source could instead be an unequal-mass or eccentric BBH. In this talk, I present explorations of (1) the hypothesized degeneracy between precession and eccentricity and (2) the complicated interplay between inferred mass ratio, total mass, and spin in GW signals from heavy BBHs. Using simulated signals consistent with GW190521, I use time-domain inference to independently constrain source parameters before and after various times in the data and link measurements of masses and spins to signal morphology. While precession, uneven masses and eccentricity can all suppress the final pre-merger cycle of a GW190521-like signal, I establish that the GW190521 data evolve over time in a manner most consistent with the precession hypothesis.